Muwatta Imam Malik Book of Shortening the Prayer, Hadith 10

Yahya related to me from Malik from Yahya ibn Said that he said to Salim ibn Abdullah, "What is the latest you have seen your father delay maghrib while on a journey?" and Salim replied, "One time the sun set when we were at Dhat al-Jaysh and he prayed maghrib at al- Aqiq."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ قَالَ لِسَالِمِ بْنِ عَبْدِ اللَّهِ مَا أَشَدَّ مَا رَأَيْتَ أَبَاكَ أَخَّرَ الْمَغْرِبَ فِي السَّفَرِ فَقَالَ سَالِمٌ غَرَبَتِ الشَّمْسُ وَنَحْنُ بِذَاتِ الْجَيْشِ فَصَلَّى الْمَغْرِبَ بِالْعَقِيقِ .